Determination of components (e.g. CO2) in a gas mixture (e.g. a breath sample) is based on the fact that gases like CO2 absorb light at a specific wavelength in the infrared light spectrum. Detection of a concentration of a gas component such as CO2 is therefore typically accomplished by passing a beam of infra-red light across the gas sample. Presence of CO2 in the gas leads to a reduction in the amount of light in the spectrum and, based upon the reduction, the concentration of CO2 in the sample is inferred.